Method of acquiring initial synchronization in impulse wireless communication and receiver

ABSTRACT

A receiver in an impulse wireless communication. The receiver ( 300 ) includes a pulse-pair correlator ( 304 ) that receives a signal ( 316 ) and divides it into two signals for paths. One of the signals is input to signal multiplier ( 312 ) while another signal is delayed by a delay unit ( 310 ). The signal multiplier ( 312 ) multiplies the received signal ( 316 ) by a delayed signal ( 318 ). An integrator ( 314 ) integrates an output signal ( 322 ) over a designated period of time. An adding module ( 306 ) sums an output signal ( 324 ) from the integrator ( 314 ). An acquiring module ( 308 ) compares an summing-up output ( 326 ) from the adding module ( 306 ) with a predetermined threshold value to detect the existence of a transmitting-standard preamble.

TECHNICAL FIELD

The present invention relates to a method of acquiring initialsynchronization and a receiving apparatus in impulse radio communicationusing a transmitted-reference preamble.

BACKGROUND ART

Recent advances in a communication technology have enabled the use oftransmitting and receiving sequences of very short-duration radiofrequency (RF) pulses, the duration of which is typically less than ananosecond. This is often referred to as “impulse radio (IR).”

There are various conventional implementations of receiving apparatusesand transmitting apparatuses for IR signals. IR transmitting apparatusesand IR receiving apparatuses can employ numerous data modulation (anddemodulation) techniques, including amplitude modulation, phasemodulation, frequency modulation, pulse-position modulation (PPM) (alsoreferred to as “time-shift modulation” or “pulse-interval modulation”)and M-ary versions of these.

At present, the most well known method is the PPM scheme. This methodworks by transmitting and receiving pulses in one of a plurality of timeslots in successive time frames, which requires close timesynchronization between the transmitting apparatus and the receivingapparatus. The PPM modulation scheme is also referred to as a “timemodulated” method, because the relativity of the arrival of the pulsesis important information that the receiving apparatus must know in orderto demodulate the transmission information.

One issue with the time modulated impulse radio transmission scheme isthe difficulty of establishing time synchronization. This is especiallytrue when the transmission information is comprised of bursts oftransmission symbols, and, in this case, the receiving apparatus has noprior information about the timing at the transmitting apparatus.

Recently, a new alternative UWB communication scheme, referred to as a“TR (transmitted-reference) scheme” has been invented. Patent Document 1discloses one such TR scheme. The term “transmitted-reference” refers tothe transmission and reception of a plurality of pulses in such a mannerthat synchronization with individual pulses is unnecessary. Pulses aretransmitted in pairs, and, in this case, the first pulse is a referencepulse and the second pulse is a data modulated pulse. The referencepulse and the data modulated pulse in each pulse pair are identical.Pulse pairs are separated or delayed from each other by time intervals,that is, by delays, which are known to the receiving apparatus.Transmitted-reference UWB transmits pulses in pairs, and thereby inducesa correlation at the receiving apparatus that can be measured bystandard means. That is, the transmitted-reference scheme does not havethe synchronization problem which occurs in the time modulated scheme.

There are several methods for acquiring synchronization using thetransmitted-reference scheme. Patent Document 2 discloses one suchmethod, where a transmitted-reference, delay-hopped (TR/DH)ultra-wideband signal is used to provide a pilot signal to acquiresynchronization. The term “transmitted-reference” maintains the samedefinition from earlier explanation. The term “delay-hopped” refers to acode-division multiple access (CDMA) scheme. Although the TR/DH schemedoes not have the problem with synchronization of the time modulatedscheme such as PPM/TH, the TR/DH scheme provides a poor signal-to-noiseratio (SNR) and is more likely to cause multiple access interference.According to performance prediction based on mathematical modeling andcomputer simulations, the influence of the multiple access interferencemay limit the multiple access capacity of the TR/DH scheme to a degreewhere it will not be suitable for some applications.

Patent Document 1: US Patent Publication No. 2003198308:“Synchronization of ultra-wideband communications using atransmitted-reference preamble.”Patent Document 2: US Patent Publication No. 2003198212: “Method andapparatus for synchronizing a radio telemetry system by way oftransmitted-reference, delay-hopped ultra-wideband pilot signal.”

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

One problem with the time modulated impulse radio transmission scheme isthe difficulty of establishing time synchronization. This is especiallytrue when the transmission information is comprised of bursts of narrowpulses in nanoseconds, and, in this case, the receiving apparatus has noprior information whatsoever about the timing at the transmittingapparatus and needs to detect the presence of the transmissioninformation prior to attempting to demodulate the transmissioninformation.

In the absence of multiple access interference (MAI), the clockgoverning the pulse slots can easily be recovered from the receivedsignal, while the frame clock must be recovered from a transmittedacquisition sequence. However, multiple access interference worsens thisproblem significantly. This is because the pulse-slot clocks of theseparate transmitting apparatuses which interfere with each other willnot be synchronized with that of the desired transmitting apparatus.This situation requires the acquisition of both the slot clock and theframe timing through the use of an acquisition sequence. The initialsynchronization requires a very large computation amount, and thiscomputational burden may result in a very long acquisition time.

Patent Document 1 discloses a method of initial synchronization thatprovides a time mark using a transmitted-reference, delay-hopped (TR/DH)burst as a preamble.

However, this method requires a bank of pulse pair correlators at thereceiving apparatus for each pulse pair transmitted in the preamble, andthis results in a very complicated structure of the receiving apparatus.

Means for Solving the Problem

It is therefore an object of the present invention to provide a novelmethod of initial synchronization acquisition in impulse radiocommunication using a transmitted-reference preamble and a receivingapparatus that simplify the structure of an impulse radio receivingapparatus by employing only one pulse pair correlator at the receivingapparatus instead of a bank of a plurality of correlators.

This method requires that, first, the transmitting apparatus sends atransmitted-reference preamble. This preamble is easily detected by thereceiving apparatus and can be processed to provide a time mark at thereceiving side of the communication system. The transmitted-referencepreamble is comprised of a series of pulse pairs transmitted as a pulsetrain, and each pulse pair is comprised of a reference pulse and a datamodulated pulse. The reference pulse and the data modulated pulse ineach pulse pair are separated by a time separation. All pulse pairstransmitted in the transmitted-reference preamble have the same timeseparation between the reference pulse and the data modulated pulse. Inthe present invention, all pulse pairs in the transmitted-referencepreamble, which represent different transmission symbols, have differentpulse duration, T_(p). This method of modulation will be referred to as“pulse width modulation” in this specification. Therefore, thetransmitted-reference preamble is modulated by pulse width modulation.

After transmitting the transmitted-reference preamble modulated by pulsewidth modulation and waiting a fixed period of time, which is known tothe receiving apparatus, the transmitting apparatus transmitstransmission data packets including transmission message data. Afterreceiving the transmitted-reference preamble, the receiving apparatuscan estimate the time of reception of the transmission data packets withthe accuracy of the time mark.

ADVANTAGEOUS EFFECT OF THE INVENTION

The present invention provides a synchronization method in the impulseradio communication system, that reduces the complexity of the structureof a receiving apparatus and hardware implementation by employing atransmitted-reference preamble sequence, which is comprised of a seriesof pulse pairs. In this transmitted-reference preamble sequence, eachpulse pair, which represents a transmission symbol, has a unique pulseduration. Compared with the structure of the plurality of correlators,this synchronization method provides a simple structure of a receivingapparatus, and the receiving apparatus in the impulse radiocommunication system requires only one pulse pair correlator having adelay circuit, a multiplier and an integrator.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a transmitted-reference preamble according to the firstembodiment of the present invention;

FIG. 2 shows a transmitted-reference preamble according to the secondembodiment of the present invention;

FIG. 3 shows a transmitted-reference preamble according to the thirdembodiment of the present invention;

FIG. 4 shows a transmitted-reference preamble according to the forthembodiment of the present invention;

FIG. 5 is a block diagram showing the configuration of a transmittingapparatus in impulse radio communication according to the presentinvention;

FIG. 6 is a block diagram showing the configuration of a receivingapparatus in impulse radio communication according to the presentinvention; and

FIG. 7 shows a structure of a burst signal and correlator outputaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

There are four embodiments for the transmitted-reference preamblesequence of the present invention. FIG. 1 shows the first embodiment ofthe transmitted-reference preamble sequence, FIG. 2 shows the secondembodiment of the transmitted-reference preamble sequence, FIG. 3 showsthe third embodiment of the transmitted-reference preamble sequence andFIG. 4 shows the fourth embodiment of the transmitted-reference preamblesequence.

FIG. 1 shows the first embodiment of the transmitted-reference preamblesequence that is communicated between a transmitted-reference impulseradio transmitting apparatus and a receiving apparatus. The number ofpulse pairs, N_(p), transmitted in transmitted-reference preamble 100Acan be any integer greater than one, and the value of N_(p) is known atthe receiving apparatus. FIG. 1 shows four pulse pairs that aretransmitted sequentially in transmitted-reference preamble sequence100A. Each pulse pair is comprised of two identical pulse waveforms,and, of these, the first pulse waveform will be referred to as a“reference pulse” and the second pulse waveform will be referred to as a“data modulated pulse.”

As shown in FIG. 1, the first pulse pair is comprised of identicalreference pulse 102 and data modulated pulse 104. The second pulse pairis comprised of identical reference pulse 106 and data modulated pulse108. The third pulse pair is comprised of identical reference pulse 110and data modulated pulse 112. The fourth pulse pair is comprised ofidentical reference pulse 114 and data modulated pulse 116.

Each pulse pair in transmitted-reference preamble sequence 100A isseparated from its neighboring pulse pairs by pulse pair interval 120,which is common in all pulse pairs in transmitted-reference preamblesequence 100A. All pulse pairs transmitted in transmitted-referencepreamble 100A have the same time separation D between the referencepulse and the data pulse.

To modulate the transmitted-reference preamble, pulse width modulationis employed. Pulse duration T_(p) of each pulse pair is used toassociate each pulse pair with a transmission symbol. As shown in FIG.1, the first pulse pair representing transmission symbol “00” has pulseduration T_(p1), the second pulse pair representing transmission symbol“10” has pulse duration T_(p2), the third pulse pair representingtransmission symbol “01” has pulse duration T_(p3) and the fourth pulsepair representing transmission symbol “11” has pulse duration T_(p4).The pulse pairs representing respective transmission symbols intransmitted-reference preamble sequence 100A must each have a uniquepulse duration.

As shown in FIG. 2, in the second embodiment of thetransmitted-reference preamble sequence, there is no difference from thefirst embodiment shown in FIG. 1, except that time separation D betweenthe reference pulse and the data pulse in transmitted-reference preamble100B is zero. The data modulated pulse is transmitted immediately afterthe reference pulse, without delay, for each pulse pair in thetransmitted-reference preamble.

FIG. 3 illustrates the third embodiment of the transmitted-referencepreamble sequence. In this embodiment, time separation D between thereference pulse and the data pulse in transmitted-reference preamble100C is not zero. The only difference between this third embodiment andthe first embodiment is that the pulse pairs representing respectivetransmission symbols can be comprised of one or a plurality of cycles ofpulse. As shown in FIG. 3, the first pulse pair representingtransmission symbol “00” is comprised of one cycle of pulse, the secondpulse pair representing transmission symbol “10” is comprised of twocycles of pulse, the third pulse pair representing transmission symbol“01” is comprised of three cycles of pulse, and the forth pulse pairrepresenting transmission symbol “11” is comprised of four cycles ofpulse.

FIG. 4 shows a transmitted-reference preamble according to the fourthembodiment. In this embodiment, pulse pair interval 120 is different foreach transmission symbol of transmitted-reference preamble 100D. Thefirst transmission symbol “00” has a pulse pair interval of T_(f1), thesecond transmission symbol “10” has a pulse pair interval of T_(f2), thethird transmission symbol “01” has a pulse pair interval of T_(f3) andthe fourth transmission symbol “11” has a pulse pair interval of T_(f4).

FIG. 2 is a block diagram showing the configuration of a transmittingapparatus in impulse radio communication, according to the presentinvention. Transmitting apparatus 200 is configured with bit generator202, channel encoder 206, impulse radio modulator 212, mappingconfigurator 214, pulse generator 218 and transmitting antenna 222.

Bit generator 202 generates digital data stream 204 from input data. Theinput data may include text data, video data, image data, audio data orcombinations of these. Channel encoder 206 performs error correctioncoding such as block coding and convolutional coding on digital datastream 204 and generates encoded data 208.

Impulse radio modulator 212 duplicates encoded data 208 and modulatesthe data in accordance with a mapping configuration set by mappingconfigurator 214 using the transmitted-reference preamble sequence,shown in FIGS. 1 to 4. Pulse generator 218 amplifies signal 216outputted from impulse radio modulator 212, generates signal 216 in apredetermined pulse shape, and transmits generated transmitted-referencepreamble 220 by radio from transmitting antenna 222.

FIG. 3 is a block diagram showing the configuration of the receivingapparatus in impulse radio communication according to the presentinvention. Receiving apparatus 300 is configured with receiving antenna302, pulse pair correlator 304, summing module 306 and acquisitionmodule 308. Pulse pair correlator 304 is configured with delay unit 310,signal multiplier 312 and finite time integrator 314.

Pulse pair correlator 304 receives signal 316 and splits the signal intotwo paths. One is directly inputted to signal multiplier 312 and theother is delayed by delay unit 310. Received signal 316 and delay signal318 from delay unit 310 are multiplied in signal multiplier 312, andnon-zero product 322 is integrated in integrator 314 over predeterminedtime, and signal 324 is generated. The integration time is equal topulse pair interval 120 shown in FIG. 1. The delay time in delay unit310 is equal to delay time D between the reference pulse and the datapulse in FIG. 1 to FIG. 4.

Summing module 306 will receive, as input, signals 324 outputted fromintegrator 314 and add all received signals. The object of thisoperation is to produce a sum of all integrated outputs of N_(p) pulsepairs in the transmitted-reference preamble sequence.

Acquisition module 308 detects the presence of the transmitted-referencepreamble sequence by comparing summed output 326 outputted from summingmodule 306 with a predetermined threshold value. The threshold value isdependent on the operating conditions. Thus, the actual value can beobtained by a person skilled in the art. In the case where summed output326 is greater than the threshold value, acquisition module 308 reportssuccessful synchronization, and, in the case where summed output 326 issmaller than the threshold value, acquisition module 308 reportsunsuccessful synchronization.

FIG. 7 shows the structure of a burst signal and correlator outputaccording to the present invention. Transmission data packet 404 istransmitted after transmitted-reference preamble 402. The receivingapparatus uses the time of maximum peak value 406 of pulse paircorrelator output detected upon reception of transmitted-referencepreamble 402 as a time mark and acquires synchronization with subsequentdata packet 404. Here, in FIG. 7, smaller peaks in the correlator outputrepresent autocorrelation side lobes and should be smaller than maximumpeak value 406.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a receiving apparatus inimpulse radio communication.

1. A method of acquiring initial synchronization in impulse radio communication, comprising the steps of: transmitting from a transmitting apparatus to a receiving apparatus a transmitted-reference preamble formed with a pair of pulses that are identically shaped and are spaced by predetermined time separation D; transmitting from the transmitting apparatus to the receiving apparatus a transmission data packet predetermined time after transmitting the transmitted-reference preamble; detecting the transmitted-reference preamble based on a correlation value between a received signal and a signal obtained by delaying the received signal by time separation D and generating a time mark at the receiving apparatus; and starting receiving the transmission data packet using the generated time mark at the receiving apparatus.
 2. The method of acquiring initial synchronization according to claim 1, wherein a pulse duration of the pair of pulses varies according to a transmission symbol.
 3. A receiving apparatus in impulse radio communication, comprising: a receiving antenna that receives a transmitted-reference preamble formed with a pair of pulses that are identically shaped and are spaced by predetermined time separation D; a delay circuit that delays the transmitted-reference preamble received by the receiving antenna by time separation D; a multiplier that multiplies the transmitted-reference preamble received by the receiving antenna by the transmitted-reference preamble delayed by the delay circuit; an integrator that integrates an output of the multiplier over a predetermined time; a summing module that sums up outputs of the integrator; and an acquisition module that detects the transmitted-reference preamble by comparing an output of the summing module with a predetermined threshold value and generates a time mark. 